Elevated r-process Enrichment in Gaia Sausage and Sequoia
Elevated r-process Enrichment in Gaia Sausage and Sequoia
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DOI：
10.3847/2041-8213/abdbb8
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发表时间：
2020-12
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通讯作者：
D. Aguado;V. Belokurov;G. Myeong;N. Evans;C. Kobayashi;L. Sbordone;J. Chanamé;C. Navarrete
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作者：
D. Aguado;V. Belokurov;G. Myeong;N. Evans;C. Kobayashi;L. Sbordone;J. Chanamé;C. Navarrete
盖亚香肠(GS)和红杉代表了形成银河系恒星晕的主要吸积事件。对这些主要构造块的详细化学研究提供了银河系组装早期步骤的原始图景。我们给出了使用Gaia DR2运动学选择的九个香肠/红杉成员在8.2米VLT处的UVES高分辨率光谱观测的分析结果。我们使用Nissen&Schuster和GALAH DR3(2020)的档案数据对这组测量数据进行季节调整。在这里，我们通过分析锶、Y、钡和Eu的行为来关注中子俘获过程。我们检测到Eu丰度([Eu/Fe]∼0.6-0.7)的明显增强，表明r过程在恒星的n俘获组成中非常普遍。我们还能够追踪各种金属丰度范围内重元素生产的演变。从[Ba/Eu]=−为0.7的紧凑、平坦的序列，反映了大质量恒星爆炸的主要贡献，转变为铁丰度更高的明显上升，揭示了来自渐近巨枝喷发的污染的开始。此外，我们在[Fe/H]−[Ba/Fe]平面上发现了两个明显的序列，可能是由不同程度的S引起的-过程污染和GS前体内部的混合。
The Gaia Sausage (GS) and the Sequoia represent the major accretion events that formed the stellar halo of the Milky Way. A detailed chemical study of these main building blocks provides a pristine view of the early steps of the Galaxy’s assembly. We present the results of the analysis of the UVES high-resolution spectroscopic observations at the 8.2 m VLT of nine Sausage/Sequoia members selected kinematically using Gaia DR2. We season this set of measurements with archival data from Nissen & Schuster and GALAH DR3 (2020). Here, we focus on the neutron-capture process by analyzing Sr, Y, Ba, and Eu behavior. We detect clear enhancement in Eu abundance ([Eu/Fe] ∼ 0.6–0.7) indicative of large prevalence of the r-process in the stellar n-capture makeup. We are also able to trace the evolution of the heavy element production across a wide range of metallicity. The barium to europium changes from a tight, flat sequence with [Ba/Eu] = −0.7 reflecting dominant contribution from exploding massive stars, to a clear upturn at higher iron abundances, betraying the onset of contamination from asymptotic giant branch (AGB) ejecta. Additionally, we discover two clear sequences in the [Fe/H]−[Ba/Fe] plane likely caused by distinct levels of s-process pollution and mixing within the GS progenitor.